1. (Field of the Invention)
The present invention relates generally to a sealed compressor for use in a refrigerator, an air conditioner or the like and, in particular but not exclusively, to pipe connectors for connecting suction and discharge pipes to a sealed casing of the sealed compressor. The present invention also relates to a method of joining the pipe connectors to the sealed casing.
2. (Description of Related Art)
FIG. 1 depicts a conventional sealed compressor having a sealed casing 101 in which a motor section 102 and a compression section 103 are both accommodated. The sealed casing 101 is provided with a suction pipe connector 104 secured thereto through which a refrigerant is introduced thereinto and a discharge pipe connector 105 secured thereto through which a compressed refrigerant is discharged therefrom. The suction pipe connector 104 and the discharge pipe connector 105 lead to an evaporator (not shown) and a condenser (not shown), respectively, to form a refrigeration cycle. Because both the evaporator and the condenser are connected to copper pipes, a material which can be readily connected to the copper pipes, for example, by copper-brazing is selected for the suction pipe connector 104 and the discharge pipe connector 105. For this reason, both the suction pipe connector 104 and the discharge pipe connector 105 are generally made of copper pipes. When each of the suction pipe connector 104 and the discharge pipe connector 105 is secured to the sealed casing 101, which is generally made of steel, it is the general practice that a portion of the pipe connector 104 or 105 is first inserted into a hole defined in the sealed casing 101 and is then rigidly secured thereto by silver-brazing with the use of flux.
More specifically, as shown in FIG. 1, the sealed casing 101 has a hole defined therein in alignment with a suction hole 106 defined in the compression section 103. An external suction sleeve 107 is inserted into the hole of the sealed casing 101 and is secured thereto. The compression section 103 also has a suction sleeve insertion hole 108 defined therein so as to be continuous to the suction hole 106. The suction sleeve insertion hole 108 is positioned radially outwardly of the suction hole 106 and has a diameter slightly larger than that of the suction hole 106. The suction pipe connector 104 includes the external suction sleeve 107 referred to above and an internal suction sleeve 109 pressed into the suction sleeve insertion hole 108 so that a low-pressure refrigerant to be introduced into the sealed casing 101 may be separated from a high-pressure refrigerant inside the sealed casing 101. The length of the internal suction sleeve 109 is determined so that an outer end thereof may be positioned radially outwardly of an outer end of the external suction sleeve 107. After a suction pipe 110 has been inserted into the internal suction sleeve 109 pressed into the suction sleeve insertion hole 108, the suction pipe 110, the internal suction sleeve 109 and the external suction sleeve 107 are simultaneously hermetically secured together by brazing, thereby separating the external atmosphere, the low-pressure refrigerant introduced into the sealed casing 101, and the high-pressure refrigerant inside the sealed casing 101 from one another.
In the above-described construction, the internal suction sleeve 109 is made of a copper pipe or a copper-plated steel pipe, while the external suction sleeve 107 and the discharge pipe connector 105 both secured to the sealed casing 101 are generally made of copper pipes. The suction pipe 110 is also generally made of a copper pipe.
The sealed compressor of the above-described construction has problem in that in applications where a copper pipe is hermetically connected to the steel sealed casing 101 by silver-brazing, flux is inevitably required, which must be removed after the brazing. Removal of he flux is generally carried out in hot water in which the flux dissolves.
On the other hand, HFC refrigerants listed as candidates for alternative refrigerants that cause no destruction of the ozone layer are generally used with an ester-based lubricant compatible therewith. The ester-based lubricant has a tendency to cause hydrolysis, which in turn produces acids. Accordingly, if a compressor contains an HFC refrigerant, it is necessary to manage the compressor so that the amount of water contained therein may be as small as possible. Furthermore, even if the amount of chlorine contained in the flux is extremely small, it acts to promote decomposition of the HFC refrigerant and that of the ester-based lubricant. Because of this, complete removal of the flux is required.
Conversely, silver-brazing requires a process in which water and chlorine-containing impurities remain that must be mostly removed during the manufacture of a compressor for use with an alternative refrigerant. In addition, it is difficult to immerse a relatively large body such as the sealed casing in hot water, and if the compressor is of a complicated structure, it is very difficult and time-consuming to completely remove water that has been used for removal of the flux.
Also, during brazing, members to be joined together must be heated to a temperature at which a brazing material melts. To this end, such members are generally heated with flames of, for example, a torch. By so doing, copper pipes as the connectors are annealed and reduced in strength. The flames produce on the members an oxide layer, which sometimes promotes deterioration of a lubricant or a refrigerant.
Furthermore, because the copper pipe connector has a relatively large thermal expansion coefficient, the pipe connector expands due to heat generated during brazing and contracts due to subsequent cooling, thus deteriorating the sealing properties between the pipe connector and the insertion hole thereof. Also, component parts of the compression section are likely to be deviated from their desired positions by relatively large forces applied thereto. If a steel pipe is used for the pipe connector, it must be finished into a desired size and then copper-plated, resulting in an increase in the manufacturing cost.